linux-kernel - Re: [RFC PATCH v3 4/6] sched: secure access to other CPU statistics

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Message-ID: <CAKfTPtA0xpGmyKr6pqiV9wjv4ZQ_xQGjR=+7h_xTe_LLA+Do9A@mail.gmail.com>
Date:	Tue, 26 Mar 2013 14:06:38 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, mingo@...nel.org,
	linux@....linux.org.uk, pjt@...gle.com, santosh.shilimkar@...com,
	morten.rasmussen@....com, chander.kashyap@...aro.org,
	cmetcalf@...era.com, tony.luck@...el.com, alex.shi@...el.com,
	preeti@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	tglx@...utronix.de, len.brown@...el.com, arjan@...ux.intel.com,
	amit.kucheria@...aro.org, corbet@....net
Subject: Re: [RFC PATCH v3 4/6] sched: secure access to other CPU statistics

On 26 March 2013 13:50, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote:
>> @@ -3364,13 +3364,16 @@ done:
>>  static bool is_buddy_busy(int cpu)
>>  {
>>         struct rq *rq = cpu_rq(cpu);
>> +       u32 sum = rq->avg.runnable_avg_sum;
>> +       u32 period = rq->avg.runnable_avg_period;
>> +
>> +       sum = min(sum, period);
>
> OK this makes sense; use a simple sanity constraint instead of going
> overboard on serialization -- however, why is this a separate patch?

There is no real reason other than explaining why I have added this
additional check

>
> That is, this could easily be part of the patch that introduces
> is_buddy_busy(); also you likely want part of this patch's changelog
> to become a comment that goes right above this min() :-)

Yes, i 'm going to do that

>
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